Impact of Cognitive Radio: Recognition and Informed Exploitation of Grey Spectrum Opportunities

In this article, we employ techniques that allow cognitive radios to familiarize themselves with an unknown spectrum environment, recognizing specific, moderately utilized spectrum bands that present an opportunity to be exploited using learning-enhanced dynamic spectrum access (DSA) techniques. Much has been made of the potential for cognitive radios to operate in white spaces, in which secondary users (SUs) avoid interference with incumbents by utilizing portions of the spectrum that remain unoccupied for fairly significant periods of time [1], [2]. However, there is also a great potential for cognitive radios to operate in gray spaces, which may be intermittently occupied or occupied by low-power interferers, requiring a degree of interference tolerance. Such spectrum opportunities, which can be exploited by cognitive radios, will not be uniform and far from it. When a spectrum opportunity arises in a band that is occupied by other users, whether the users are licensed or not, the behavior of the users' networks determine what, if any, spectrum will be available to the secondary cognitive radio user. If the cognitive radio can learn how the other users are exploiting the spectrum, then it can make a more informed attempt to exploit the opportunity. In this article, we examine the possibility of exploiting gray space opportunities in global system for mobile communications (GSM), digital-enhanced cordless telecommunications (DECT), and 2.4-GHz industrial, scientific and medical (ISM) bands.